Three dimensional (3D) rendering is the computer graphics process of automatically converting 3D wire frame models into two dimensional (2D) images with 3D photorealistic effects or non-photorealistic rendering on a computer. A wire frame model is a visual presentation of a 3D or physical object used in 3D computer graphics. A scene description language can be used to describe a scene that is to be rendered by a 3D renderer into a 2D image. In the process of rendering a 2D image of a scene out of a 3D scene description, each pixel for the 2D image may receive contributions (e.g., image fragments) from multiple objects in the scene. In order to produce a single color value for each pixel, these image fragments are generally combined together in a process that is usually referred to as “compositing”. To correctly account for occlusion (e.g., hidden objects), foreground fragments should generally fully occlude the background fragments. If the foreground fragments are semi-transparent, the foreground fragments should be composited on top of the background fragments using a physically-based blending technique, such as an “over” operation. Depending on which order the fragments are composited in, a different result for the pixel color may be obtained. The 3D scene description can be inaccurate, and as the scene is animated, small errors in the surface positions may cause the fragment order to change abruptly. Such sudden changes may cause large discontinuous changes in the final color of the composited pixel, showing up as sptial aliasing in a 3D image or flickering in a video.